Patent Document 1 describes an engine automatic stop and restart device for use with an idling stop-capable vehicle that restarts using a starter, the device having a starter pinion gear engaged with an engine ring gear beforehand to shorten the time required to restart the engine from an idling stop state.
Patent Document 2 describes an engine starting device which, as a measure to reduce noise upon engine startup, causes the pinion gear and the ring gear to be engaged gently with each other while the engine is being stopped before getting started.
Vehicles equipped with the techniques of Patent Document 1 or 2 have the pinion gear and the ring gear kept engaged with each other when stopped. When restarted after being inactive for an extended period of time especially in cold regions, such vehicles may fail to get the pinion gear and the ring gear disengaged from each other due to freezing, which can result in a failure.
As a measure to avoid such an eventuality, Patent Document 3 describes a technique which, when the ignition system of the vehicle is turned off, disengages the pinion gear from the ring gear using a pinion drive means for causing the pinion gear to slide over the ring gear along an output rotation shaft, thereby preventing a failure stemming from the pinion gear being stuck with the ring gear at the next restart.